STATEN ISLAND, N.Y. -- The empty rooftop of a Department of Environmental Protection wastewater treatment plant in Port Richmond will soon be the home of hundreds of solar panels, Deputy Mayor Caswell Holloway announced Monday.

"We are here today to mark the start of a public-private partnership that's been long in the works, for the installation of nearly two megawatts of solar power right here on this roof," Holloway said.

The Port Richmond rooftop will be the largest of four solar panel installations citywide -- together they'll produce enough energy to power about 245 residences and decrease greenhouse gas emissions by 1,636 metric tons a year.

The other sites for the program are a Staten Island Ferry maintenance building in St. George, and Herbert Lehman and John F. Kennedy high schools in the Bronx.

City officials said the solar panels will help the city reach goals set by Mayor Michael Bloomberg for the PlaNYC program, which calls for reducing greenhouse gas emissions citywide by 30 percent by 2017.

"Part of the way you do that is you go from less carbon-intensive ways of powering facilities to no-carbon intensive ways, like solar power," Holloway said of the mayor's goal.

The solar panels on the roof will generate about 10 percent of the plant's total power each year -- and while that may seem like a small fraction, it's 10 percent of the plant's power that will no longer be competing with other needs on the city's power grid.

Holloway said taking that power off the grid when people are cranking up their air conditioners will reduce the chance of blackouts.

The city will have no upfront capital cost in installing the panels -- Tangent Energy Solutions of Pennsylvania will instead find the financiers for the project. The city will not own the panels but will purchase the energy generated from it. The partnership will save the city more than $8 million compared to installing the solar panels through its own capital construction program, city officials said.

In addition to reducing greenhouse gases, the project will create 40 new green jobs, Holloway said.

Edna Wells Handy, commissioner of the Department of Citywide Administrative Services -- which pays the city's electric bills -- said the project had been a long time coming. "The solar power program is a true citywide effort," she said.

Dave Turner, COO of Tangent, said the solar panels on the Port Richmond roof could cover one and a half football fields. He said the company's expertise is helping large energy users -- like the City of New York and the DEP plant in particular -- integrate clean energy generation into their systems.

"On hot summer days when energy demand reaches peak levels, centralized generation is maxed out and transmission distribution lines are stressed, distribution generation facilities like these provide a cost-effective way to maintain system reliability without relying on costly fossil fuels," he said.

The 200,000-square-foot roof has already been equipped with a white geomembrane making it what's known as a "cool roof."

"It's the largest cool roof in the city," Strickland said. "It lowers the temperature and reflects back sunlight, it doesn't absorb it, and this will help out the solar panels because it will increase their efficiency."

The Port Richmond facility alone could power 169 homes a year, the city said. The project is still in the design phase, but installation of the solar panels will begin over the summer. ---Follow @siadvance on Twitter